C++ Vector Library - capacity() Function

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Description

The C++ function std::vector::capacity() returns the size of allocate storage, expressed in terms of elements.

This capacity is not necessarily equal to the size of vector. It can be equal or greater than vector size.

The theoretical limit on vector size is given by member max_size.

Declaration

Following is the declaration for std::vector::capacity() function form std::vector header.

C++98

size_type capacity() const;

C++11

size_type capacity() const noexcept;

Parameters

None

Return value

Returns the size of allocate storage, expressed in terms of number of element can be held by vector.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::vector::capacity() function.

#include <iostream>
#include <vector>

using namespace std;

int main(void) {
   vector<int> v;

   for (int i = 0; i < 5; ++i)
      v.push_back(i + 1);

   cout << "Number of elements in vector = " << v.size() << endl;
   cout << "Capacity of vector           = " << v.capacity() << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

Number of elements in vector = 5
Capacity of vector           = 8